BEHAVIOUR OF M 25 GRADE CONVENTIONAL CONCRETE AND FLY ASH BLENDED CONCRETE IN ACIDIC ENVIRONMENT

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1 BEHAVIOUR OF M 25 GRADE CONVENTIONAL CONCRETE AND FLY ASH BLENDED CONCRETE IN ACIDIC ENVIRONMENT R Rajesh Kumar 1, P Jeevana 2, M Harsha Vardhan Reddy 3, E Eswar 4, S Gowri Shankar 5 1 Assistant Professor of Civil Engineering Department, Siddharth Institute of Engineering & Technology, Puttur A.P, India 2,3,4,5 Under Graduate Student, Civil Engineering Department, Siddharth Institute of Engineering & Technology, Puttur A.P, India ABSTRACT Concrete is highly susceptible to acid attack because of its alkaline nature and it is a serious issue due to speed of damage of concrete structures worldwide. The acid attack on the concrete structures is increasing due to growing activities in both urban and industrial areas over the past 3-4 years. The present investigation is mainly aim to study the variation in compressive strength and mass of M 25 grade Conventional Concrete (CC) and Fly Ash blended Concrete (FC_2, FC_3) mixes after 3 and 6 days of immersion in acid after 28 days of initial curing. Concrete mixes were subjected to two acid attacks i.e.., 3% Hydrochloric Acid (HCl) and 3% Sulphuric Acid (H2SO4). KEYWORDS: M 25 Grade concrete, HCl, H2SO4, Compressive Strength and mass. 1. INTRODUCTION Various industries produce numerous solid waste materials. The disposal of these solid waste materials is an environment hazard for the surrounding living beings. Now a day s increasing environmental concerns and sustainable issues, the utilization of solid waste materials is the need of the hour. The productive use of solid waste materials is the best way to alleviate the problems associated with their disposal. The construction industry has enormous potential for the use of solid waste materials as construction material. Based upon their properties, the solid waste materials can either be used as supplementary cementitious materials or as replacement of fine/coarse aggregate in concrete or mortars. Based on the research reports some solid waste materials such as fly ash, silica fume, grounded blast furnace slag etc have been put in use in manufacturing of either cement or concrete. The rate of hydration in fly ash is generally very slow. As a result, the strength gain is very slow, but continues with time over the years. The pozzolanic property of fly ashes is taken advantage of while replacing cement partially with fly ash in cement concrete. Partial replacement of cement in concrete with fly ash leads to several advantages. Fly ash is finely divided waste by product obtained from the combustion of pulverized coal in suspension fired furnaces of thermal power plants. It is collected by electrical or mechanical precipitators including cyclone precipitators or bag houses. It is generally finer than cement and consists of mostly spherical glassy particles of complex chemical as well as mineralogical composition. 2. LITERATURE REVIEW This chapter discusses the research work carried out on concrete using industrial wastes materials and various acids. This chapter gives a comprehensive review of the work carried out by various researchers in the field of reusing the industrial wastes materials in concrete. Emmanuel K. Attiogbe and Sami H. Rizkalla concluded that increase in sulphur content of test specimens, as measured with an SEM equipped with an energy-dispersive x-ray analyzer, is a good indicator of the extent of 35

2 damage in concrete due to exposure to sulphuric acid. Photomicrographs, as well as the variation in sulphur concentration with distance from the acid-exposed Surface of test specimens, clearly show that deterioration of concrete due to sulphuric acid attack starts at the surface and progresses inwards. The increase in thickness (expansion) of small specimens (with large surface area-tovolume ratios) may be a more consistent measure than the weight loss of larger specimens when comparing the effects of different sulphuric acid concentrations on concrete. The relationship between degree of concrete deterioration and depth of penetration of sulphuric acid could be represented by the variation in sulphur concentration. Salim Barbhuiya and Davin Kumala concluded that in sulphuric acid environment, the compressive strength loss was minimum for a concrete mix in which cement was replaced with 3% fly ash and 1% ultra-fine fly ash. The mass loss was less in this mix compared to the mix without fly ash. However, mass loss was also less in mixes containing higher amount of fly ash. The SEM image of concrete mix with 3% fly ash and 1% ultra-fine fly ash cured in water for 28 days showed denser microstructure characterized by less amounts of calcium hydride crystals. The SEM images of concrete mix containing 3% fly ash and 1% ultra-fine fly ash exposed to sulphuric acid for 28 days showed that the surface is highly porous. A noticeable amount of C-S-H gel appears to have been decomposed into finer particles. B. Madhusudhan Reddy, H. Sudarsana Rao and M.P George concluded that both initial and final setting times of fly ash based (BC) and silica flume blended cement (SFBC) got retarded with an increase in hydrochloric acid concentration in deionized water. Continuous decrease in compressive strength BC and SFBC specimens prepared with HCl acid solution is observed as the acid concentration increases till the maximum concentration tested. 3. EXPERIMENTAL PROGRAMME 3.1 Materials Constituent materials used to make concrete can have a significant influence on the properties of the concrete. The following sections discuss constituent materials used for manufacturing of both conventional concrete (CC) and Fly Ash (FC) based concrete. Chemical and physical properties of the constituent materials are presented in this section Cement Ordinary Portland Cement 53 grade was used corresponding to IS (1987). The physical properties of the cement as obtained by the manufacturer are presented in the Table 3.1. Table 3.1 Physical Properties of Cement Physical properties Test result Specific gravity 3.15 Fineness (m 2 /Kg) Normal consistency 3% Initial setting time (min) 9 Final setting time (min) 22 Soundness Lechatelier Expansion (mm) Autoclave Expansion (%) Compressive strength (MPa) 3 days 7 days 28 days Fly Ash The physical properties of the Fly Ash as obtained by the manufacturer are presented in the Table 3.2. Table 3.2 Physical properties of Fly Ash Material Specific gravity Fineness (m 2 /kg) Water absorption (%) Fly Ash Coarse aggregate Crushed granite stones of size 2 mm used as coarse aggregate. The bulk specific gravity in oven dry condition and water absorption of the coarse aggregate 2 mm per IS 2386 (Part III, 1963) are 2.6 and.3% respectively. The bulk density, impact strength and crushing strength values of 2 mm aggregate are 158 kg/m3, 17.9% and 22.8% respectively Fine aggregate Natural river sand is used as fine aggregate. The bulk specific gravity in oven dry condition and water absorption of the sand as per IS 2386 (Part III, 1963) are 2.6 and 1% respectively. Fineness modulus of sand is Water Generally, water that is suitable for drinking is satisfactory for use in concrete. When it is suspected that water may contain sewage, mine water, or wastes from industrial plants or 36

3 canneries, it should not be used in concrete unless tests indicate that it is satisfactory. Water from such sources should be avoided. 3.2 Test Methods This section describes the test methods that are used for testing the hardened properties of concrete Compressive strength test Compressive strength test was conducted on the cubical specimens for all the mixes at different curing periods as per IS 516 (1991) shown in fig 3.1. Three cubical specimens of size 15 mm x 15 mm were cast and tested for each age and each mix. The compressive strength (f c) of the specimen was calculated by dividing the maximum load applied to the specimen by the cross-sectional area of the specimen. Table 3.3 Concrete quality grading as per BIS (Part-I) Pulse velocity (m/s) Concrete quality grading Above 45 Excellent Good 3-35 Medium Less than 3 Doubtful Fig.3.1 compressive strength of cubes Pulse Velocity The test involves determination of pulse velocity through concrete as per procedure give in ASTM C Battery operated Portable Ultrasonic Non-destructive Digital Indicating Tester was used to measure the pulse velocity through concrete. Pulses of longitudinal stress waves are generated by an electro acoustical transducer held in contact with one face of concrete and are received by another transducer held in contact with other face of concrete specimen. The time (T) taken by pulse to pass through specimen of length (L) is known as transit time. The pulse velocity (V) is calculated by dividing the length of specimen (L) by transit time (T). Average value of three specimens was considered as the pulse velocity of concrete mix. The apparatus set for the test is shown in Fig 3.2 and values of pulse velocity for grading concrete as per BIS (Part-I) are given in Table 3.3. Fig.3.2 Ultrasonic Pulse Velocity test of cubes Acid Resistance Resistance of concrete specimens against external acid attack was evaluated as per ASTM C The specimens were identified using plastic numbers fixed with the help of adhesive. Each specimen of concrete was weighed on completion of initial water curing period of 28 days. Then the specimens were immersed in 3% sulphuric acid solution and 3% hydrochloric acid. During this test the changes in the following properties of specimens were determined after 3 and 6 days of immersion the specimens in 3% sulphuric acid solution and 3% hydrochloric acid. The Figs. 3.3 and 3.4 show the deterioration of specimens after 3 and 6 days of immersion in sulphuric acid solution and hydrochloric acid respectively. Weight of specimen Appearance of specimen Compressive strength Fig.3.3 Cubes after acidic attack (H 2SO 4) 37

4 CC FC_2 FC_3 Fig. 3.6 Cubes after acidic attack (HCl) 3.3 Design Table 3.4 Proportions of CC, FC_2 and FC_3 Compressive strength(mpa) Acidic immersion period(days) 3 6 Nor mal curi ng peri od(2 8 days ) Ce me nt Kg/ HC l Fly Ash Kg/ H 2S O Wat er l/ HC l m m kg/ H 2S O San d kg/ 113 CC FC_ FC_ This section describes the proportions of M 25 grade conventional concrete mix proportions as per IS 1262 (29) and IS 456 (2) shown in Table RESULTS AND DISCUSSIONS 4.1 Introduction In this Chapter, the test results are presented and discussed. The test results cover the performance of Conventional Concrete (CC) and Fly Ash blended Concrete (FC_2), (FC_3) in acid environment. The hardened properties of CC and FC viz. compressive strength, weight, ultrasonic pulse velocity (UPV) and rebound hammer test were determined before and after acid attack at different curing periods. 4.2 Variations in Compressive Strength The variations in compressive strength values after acid attack are represented in below. Table 4.1 shows the compressive strength of CC, FC_2 and FC_3 (Cement replaced with 2% and 3 % of Fly Ash in CC). Table 4.1 compressive strength of concrete mixes The variations in percentage loss of compressive strength values after acid attack are represented in table 4.2. Table 4.2 percentage loss of compressive strength of concrete mixes Loss of compressive strength (%) Acidic immersion period (days) 3 6 HCl H 2SO 4 HCl H 2SO 4 CC FC_ FC_ From the Tables 4.1 and 4.2, it is seen that the compressive strength of all concrete mixes have been decreased with the increase in the immersing period in each acid environment. The percentage loss of compressive strength is higher in FC_2 when compared to CC at all acid immersion periods. But it is noted that in FC_3 reduced this percentage loss when compared to FC_2. It may be due to the high pozzolanic action of fly ash which densifies the pore structure of the mix that leads to the enhancement of micro level and macro level properties. As it can be seen from the results, the percentage loss of compressive strength is marginally similar in both the CC and FC_3 concrete mixes. The percentage loss of compressive strength is observed to be more in H2SO4 than HCl. % LOSS OF COMPRESSIVE STRENGTH CC FC_2 FC_ HCL H2SO4 HCL H2SO4 3 6 CURING PERIOD Fig. 4.1 percentage loss of compressive strength of concrete mixes 38

5 4.3 Variations in Mass The variations in mass after acid attack CC FC_2 FC_3 are represented below. Table 4.3 shows the mass of CC, FC_2 and FC_3 (Cement replaced with 2% and 3 % of Fly Ash in CC). Table 4.3 Mass of concrete mixes Mass(kg) Acidic immersion period (days) HCL H2SO4 HCL H2SO CC CURING PERIOD FC_2 FC_ The variations in percentage loss of mass values after acid attack are represented. Table 4.4 shows the mass. Table 4.4 percentage loss of mass of concrete mixes Loss of mass (%) Acidic immersion period (days) 3 6 HCl H2SO4 HCl H2SO4 CC FC_ FC_ From the Tables 4.3 and 4.4, it is seen that the mass of all concrete mixes have been decreased with the increase in the immersing period in each acid environment. The percentage loss of mass is higher in FC_2 when compared to CC at all acid immersion periods. But it is noted that the incorporation of FA in FC_3 reduced this percentage loss when compared to FC_2. It may be due to the pozzolanic action of fly ash which defines the pore structure of the mix that leads to the enhancement of micro level and macro level properties. As it can be seen from the results, the percentage loss of mass is marginally similar in both the CC and FC_3 concrete mixes. The percentage loss of mass is observed to be more in H2SO4 than HCl. % LOSS OF MASS Fig. 4.2 percentage loss of mass of concrete mixes 5. CONCLUSION This chapter summarizes the overall conclusions drawn from the investigation of concrete using fly ash (cement replaced with fly ash). The following conclusions have been drawn from the present investigation. 1) The loss of compressive strength and mass values are more in FC_2 when compared to CC at all immersion periods due to more deterioration of aggregates. 2) It is noted that the increase of FA in FC_3 reduced the percentage loss when compared to FC_2. It may be due to the high pozzolanic action of fly ash which densifies the pore structure of the mix that leads to the enhancement of micro level and macro level properties. This pozzolanic action compensates the deterioration caused by aggregates. 3) It is seen that the percentage loss of compressive strength and mass of all concrete mixes have been decreased with the increase in the immersing period in each acid environment. 4) The loss of compressive strength and mass value of all concrete mixes is more in H2SO4 when compared to HCl immersion. REFERENCES ASTM C 618. American Society for Testing and Materials. Standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete, 23. IS: Specification for 53 grade ordinary Portland cement, Bureau of Indian Standards, New Delhi (India). IS: Part III. Methods of test for aggregates for concrete. Specific gravity,

6 Density, Voids, Absorption and Bulking, Bureau of Indian Standards, New Delhi. IS: Concrete Proportioning Guidelines, Bureau of Indian Standards, New Delhi (India). IS: Plain and reinforced concrete code for practice, Bureau of Indian Standards, New Delhi (India). IS: Methods of tests for strength of concrete, Bureau of Indian Standards, New Delhi (India) 4